In the bowl of a mixer, beat butter until smooth and whipped.
Add in powdered sugar and mix completely.
Add in vanilla extract, chocolate, cocoa, and heavy cream and whip until smooth and creamy.
Be sure to scrape down sides so it's all mixed in.
Add frosting to a piping bag fitted with a 2D tip (or star tip of your choice) and pipe frosting onto completely cooled cookies.
I start in the center of each cookie and press some frosting out then make a swirl around the center a full circle almost to the outer edge of each cookie.